Don't be dazzled by psi, or you may end up with plenty of pressure but not enough flow. Instead, calculate cleaning units (CU) by multiplying psi by gpm. This factor better represents the cleaning power you really have. The higher the CU, the deeper you can clean and the faster it'll go.
Pro TIP: "Run an $8 can of Pump Saver through your pressure washer before storing it for the winter to protect the pump and keep the seals from drying out." —Bill Mikenis, Pressure Washers Direct